Black hole formation in the early universe

TL;DR

This study uses high-resolution cosmological simulations to investigate the direct collapse scenario for early supermassive black hole formation, demonstrating that turbulent accretion can produce black hole seeds of around 1000 solar masses that grow rapidly.

Contribution

It presents the highest resolution simulations to date, analyzing the impact of turbulence on black hole seed formation during direct collapse in the early universe.

Findings

Central objects reach ~1000 solar masses within 4 free-fall times.

Fragmentation occurs but does not hinder central object growth.

Black hole seeds can grow up to 10^6 solar masses in about 1 million years.

Abstract

Supermassive black holes with up to a $\rm 10^{9}~M_{\odot}$ dwell in the centers of present-day galaxies, and their presence has been confirmed at z $\geq$ 6. Their formation at such early epochs is still an enigma. Different pathways have been suggested to assemble supermassive black holes in the first billion years after the Big Bang. Direct collapse has emerged as a highly plausible scenario to form black holes as it provides seed masses of $\rm 10^{5}-10^{6}~M_{\odot}$. Gravitational collapse in atomic cooling haloes with virial temperatures T$_{vir} \geq 10^{4}$~K may lead to the formation of massive seed black holes in the presence of an intense background UV flux. Turbulence plays a central role in regulating accretion and transporting angular momentum. We present here the highest resolution cosmological large-eddy simulations to date which track the evolution of high-density regions on scales of $0.25$~AU beyond the formation of the first peak, and study the impact of subgrid-scale turbulence. The peak density reached in these simulations is $\rm 1.2 \times 10^{-8}~g~cm^{-3}$. Our findings show that while fragmentation occasionally occurs, it does not prevent the growth of a central massive object resulting from turbulent accretion and occasional mergers. The central object reaches $\rm \sim 1000~M_{\odot}$ within $4$ free-fall times, and we expect further growth up to $\rm 10^{6}~M_{\odot}$ through accretion in about 1 million years. The direct collapse model thus provides a viable pathway of forming high-mass black holes at early cosmic times.